It is the image shoppers use to answer "will this look right on me?". Length, where a waist sits, how a sleeve breaks at the wrist: none of that reads on a hanger. Brands usually want more than one body type too, so customers of different sizes can see themselves in the photos.
A conventional on-model shoot books models, a stylist, hair and makeup, a photographer and a studio, and every new product waits for the next shoot day. Faces change between seasons and the catalogue drifts. That cost and that wait are why many brands still list some products with flat lays alone.
